SANTA CLARA, Calif. — The NFL’s goal to be the first major professional sports league to implement testing for human growth hormone appears a long way from coming to fruition.

NFLPA executive director DeMaurice Smith said Thursday that players have serious questions about the safety and reliability of the test. He said the World Anti-Doping Agency has not turned over the information the players’ association has requested.

“The one thing that we don’t know is what that population test looks like,” Smith told The Associated Press after addressing students during a sports law symposium at Santa Clara University. “Who was included in that study? What were the ratio levels?

“Were they tested, or was that population tested in conditions or similar situations that would mirror professional football athletes? I don’t know. And that’s information that they (WADA) refuse to turn over.”

HGH is naturally occurring in the body. The isoform test first used by WADA in 2004 — and which

became more widespread in 2008 — is designed to detect synthetic HGH by measuring the ratio naturally occurring in the body against a population test.

WADA handles drug testing for the Olympics and is largely accepted as the gold standard for worldwide drug testing. Smith said he is concerned that it does not take into account the different types of bodies and conditions for football players.

“We made a number of requests for WADA, specifically about the scientific justifications for the test that they provide,” Smith said. He would not elaborate on the other requests or set a timetable for the union’s plans.

Blood testing for HGH was part of the collective bargaining deal struck between the league and players this summer — but only if the union agreed to the methods. NFL Commissioner Roger Goodell sent a letter to Smith last week reiterating the league’s eagerness to implement HGH testing.

The NFL also notified teams that no HGH testing will be conducted before the season begins because the players’ association could not agree to the terms. The league has long disputed the union’s claims that the test is not valid.

“We have the same information as the union, and there is no question among the experts and scientists about the validity of the test,” NFL spokesman Greg Aiello said. “But if you’re trying to avoid making a decision, one way is to keep asking for more information.”

Members of Congress also have urged the two sides to come to an agreement.

In a letter to the league and the players’ association Thursday, Rep. Henry Waxman, D-Calif., encouraged both to resolve their differences so that testing can begin sometime this season, which opened Thursday night in Green Bay.

“While blood testing for HGH involves a relatively new technique, there are virtually no questions about the scientific credibility of this testing methodology,” Waxman wrote. “The test is approved and used by the World Anti-Doping Agency, has been used for Olympic testing, and earlier this month was used in the United States to identify a professional athlete using the drug.”